The present invention belongs to a technical field of an inkjet printer that ejects ink droplets to record an image. More particularly, the present invention relates to an inkjet recording head, a method of manufacturing the same and an inkjet printer using the inkjet recording head, whose yield of production can be greatly improved.
An inkjet recording apparatus is disclosed in Japanese Patent Laid-Open No. Sho48(1973)-9622 gazette and No. Sho54(1979)-51837 gazette, in which a portion of ink is rapidly evaporated by a pulse heating and ink droplets are ejected from orifices by expansion force.
In the inkjet recording apparatus, the simplest method of the pulse heating is the one in which pulse energizing is applied to a thin film heater.
Forming a drive LSI to perform the pulse conduction and the thin film heater on the same silicon (Si) substrate can realize a small and high thermal efficient inkjet recording head that has never existed before. Such an inkjet recording head is disclosed by one of the present inventors in Japanese Patent Laid-Open No. Hei6(1994)-71888 gazette, No. Hei6(1994)-297714, No. Hei7(1995)-227967, No. Hei8(1996)-20110 and No. Hei8(1996)-207291.
Using this technology can allow the orifices for ink ejection to be integrated and formed two-dimensionally in a large scale and in high-density. For example, a full-color printer for A4 paper having a recording capability of 30 ppm to 60 ppm (currently, several ppm)(ppm represents pages per minute).
FIG. 8 shows a schematic sectional view of one example of such a conventional inkjet recording head.
An inkjet recording head (hereinafter, referred to as a recording head) 150 shown in FIG. 8 has drive LSIs 14 directly formed on the surface (a side where nozzles are formed, to be described later) of an Si substrate 12. In addition, heat generating resistors (not shown) driven by the drive LSIs 14, partition walls 15 that form ink flow paths for supplying ink to nozzles and the like are also formed on the surface of the Si substrate.
Moreover, ink grooves 16 for supplying ink to the ink flow paths are formed on the Si substrate 12 in an extended manner in an array direction (a perpendicular direction to the paper surface of FIG. 8) of the nozzles so as to dig into the surface of the Si substrate 12. Further, ink supply bore holes 18 for supplying ink to the ink groove 16 are arrayed at specified intervals in the extending direction of the ink groove 16 and bored so as to communicate the back surface of the Si substrate 12 and the ink groove 16.
Orifices 20 functioning as nozzles for ink ejection are formed on an orifice plate 22 laminated on the Si substrate 12 (partition walls 15). The nozzles, each of which is circular in section, are arrayed in the perpendicular direction to the surface of this paper, for example, in a pitch of about 70 μm (360 npi=nozzles per inch). As shown in FIG. 8, the recording head of 720 npi can be realized by including two of such nozzle arrays.
Ink is led from the ink supply bore hole 18 formed on the Si substrate 12 into the ink groove 16 on the upper surface of the substrate. Ink, then, flows through the ink flow path formed by the partition wall 15, is distributed to the orifice arrays (nozzle arrays) formed on the both sides (perpendicular direction to the nozzle array) of the ink groove 16 in 360 npi, and is ejected.
Note that reference numeral 24 in the drawing denotes a frame for supporting the Si substrate 12. Ink grooves 26 are formed in the frame 24 for supplying ink, which is supplied from ink tanks via specified routes formed on the inkjet recording head is supplied to the ink supply bore holes 18 thorough the ink grooves 26. Hereinafter, in FIG. 8, a component except for the frame 24 shall be referred to as a chip (that is, a head body) 152.
The chip 152 of the recording head 150 can be fabricated by a thin film forming process used in a semiconductor manufacturing or the like. Therefore, the large number of chips 152 can be formed on one piece of an Si wafer as shown in FIG. 9A.
As shown in FIG. 9B, a nozzle array 28Y, a nozzle array 28C, a nozzle array 28M and nozzle arrays 28B (two arrays) are formed on one chip 152, which are made by arraying the orifices 20 (nozzles) that eject yellow ink (Y), cyan ink (C), magenta ink (M) and black ink (B) respectively (the foregoing FIG. 8 shows a sectional view of FIG. 9B at line a—a).
Therefore, four ink supply bore holes 18 (18Y, 18C, 18M and 18B) are formed on the chip 152, that is, on the back side of the Si substrate, each of which supplies ink to each ink groove 16 of each nozzle array 28 in an example shown in the drawing.
As described above, since the nozzles are arrayed in 360 npi, one scanning can form a full color image of about 9 mm width by allowing one nozzle array 28 to have 128 nozzles, for example.
Moreover, printing speed can be greatly improved when a long head (a line head) as shown in FIG. 10 is fabricated. For example, a line head having nozzle arrays exceeding 190 mm can produce a color image of size A4 in one scanning.
As described above, the head 150 is small and has high thermal efficiency and superior capability. However, on the contrary, there is a problem that the strength of the chip 152 is low and production yield thereof is reduced.
As described above, the ink grooves 16 and the ink supply bore holes 18 are formed in the chip 152. The ink groove 16 is formed by digging into the surface of the Si substrate 12 (Si wafer) so as to extend over the entire length of the nozzle array 28. Moreover, in the ink groove 16, the depth and the width of a certain extent are required to reduce a flow path resistance in order to eject ink in good condition.
In addition, the ink supply bore holes 18 are made by boring to penetrate the Si substrate 12. Similarly to the ink grooves 16, the diameter and the number thereof to a certain extent are required to reduce the flow path resistance.
Due to the ink grooves 16 and the like, the strength of the Si substrate 12, which is not very high originally, further reduces. Particularly, the strength reduction greatly emerges in the line head shown in FIG. 10 because of its long size.
As a result, heat, mechanical stress and the like cause a crack in the Si substrate 12 and the chip 152. Such heat, mechanical stress and the like occur on occasions for: adhesion step of the orifice plate 22; cutting off the chip 152 from the Si wafer; handling the chip 152 after cutting off; fixing and wire connecting the chip 152 onto the frame 24 (when the chip 152 is mounted on the frame 24) and the like. In the extreme case, the chip 152 is broken, and such a crack and a break are causes for the yield reduction of the recording head 150.